End-to-End Simulation of On-Orbit-Servicing: Technical implementation of communications

The robotic on-orbit servicing technology promises an increase in life-time of operational satellites and the removal of space debris. Though such tasks are of high importance for future space exploration in general, many agencies and companies struggle with running such missions. One of the reasons is definitely to find the ultimate business case. Moreover, on-orbit servicing imposes very high risks on a mission due to its complexity which is almost as high as in human space flight. It is therefore essential to perform end-to-end hardware-in-the-loop simulations of a mission on ground before it is being carried out in space. For this purpose, the On-Orbit-Servicing End-to-End Simulation project (OOS E2E) has been established at the German Aerospace Center (DLR). The project uses expertise, resources and facilities from a couple of DLR institutes. Contributors are the German Space Operations Center (GSOC), the Institute of Robotics and Mechatronics (RM) and the Institute of System Dynamics and Control (SR). The aim of the On-Orbit-Servicing End-to-End Simulation project is to connect the different simulation facilities of these institutes and integrate them into a single end-to-end simulation of on-orbit servicing. One of the facilities is the European Proximity Operations Simulator (EPOS) to simulate the rendezvous maneuver between the client satellite and the chaser satellite. The other facility is the On-Orbit-Servicing Simulator (OOS-Sim) of the Institute of Robotics and Mechatronics to simulate the robotic telepresence operations. In this paper we focus on the implementation of data communication between all of the simulation facilities. Especially, the need for real-time robotic telepresence operations creates a new set of requirements for the communication chain. To account for a real- world scenario, it is therefore important to simulate the communication chain and the operational environment of an on-orbit servicing mission. The behavior of the space link, as well as the data transportation on ground, must be taken into account, including all communication parameters like possible loss, delay, jitter, corruption or duplication in the TM/TC data streams. As these parameters vary over time, the occurrence of bursts and the timely distribution of these parameters play a significant role. Furthermore, the beginning, the end and possible handovers of a satellite passage must be simulated. As the robotic telepresence operations are as important as the housekeeping operations, the setup must be optimized for processing both robotic real-time data and standard satellite TM/TC data in parallel. To do so, both data streams must be multiplexed into a single space link. This is done by specially developed FPGA devices that can be synchronized to a common master clock to multiplex/demultiplex both data streams into/from a single space link in a timely manner. Furthermore, Space Link Protocols have to be implemented between the space and ground components of the simulation. In the same way, the protocols of the ground segment must be optimized for the processing of real-time data. For this purpose, a common Space Link TM/TC library has been developed in C++, which is being shared between the European Proximity Operations Simulator (EPOS), the On-Orbit-Servicing Simulator (OOS-Sim), the satellite simulator, the dynamic simulator, the robotic console, the rendezvous console, the satellite console and the standard TM/TC chain for housekeeping. To operate the distributed simulation system in a reliable way, it is further necessary to implement a monitoring and control software. For this purpose, we use an instance of an already established Antenna Monitoring and Control Framework that is used at the Ground Station Weilheim. In this paper we present the technical implementation of the communication chain of the project and results of performance test measurements. In particular we analyze the real-time requirements for the setup. Finally, we discuss future improvements and how the setup can be adopted to a real-world scenario. A demonstration video of a full end to end simulation is also presented.